Spambot = DOS

This is getting serious. Yesterday night a spammer put 245 comments in less than 2 minutes to some MovableType blogs I host. The result: the server got overloaded in no time and the kernel started a great massacre in there. After the smoke cleared up crond, named and munin-node were killed - for the whole night, I just restarted them. It's really pissing me off, an automated process can bring down a server in 2 minutes, I'll have to do something about this. Ideas:

• upgrade to MT3, check how it's done there
• disable comments for old posts (is it possible in MT2.6?)
• hack comments.cgi not to allow more than 1 comment / 1 minute / 1 IP
• replace MTBlackList with a better protection tool

That's all I can think of. Together with the previous trouble with MT2.6 I think it might be time to upgrade.